Hi all,
I can't seem to find the answer to this question using the search. I have seen this diagram:

My question concerns the thick and thin spacers. If I remember correctly, when cleaning my thermostat, it had at least 2 thick spacers and 1 or 2 thin spacers. Either way, I know it was more than 1 of each. Is it possible for this to be correct, or was someone in the past trying to adjust the mixture using these spacers? Should I remove the extra ones?

Okay, I went home and took it off to have another look. Here's what I found:

The spacers were placed on the paper in the order they came off the rod (#1 being closest to the thermal discs). Its hard to judge the size of them in the pic, but numbers 1, 2, and 4 are the same size (thinnest). Numbers 3 is the next size up, then number 6, and number 5 is the thickest.

If anyone knows which ones I should eliminate, if any, please chime in.

Another thing I have noticed while preparing to adjust my mixture... I can't seem to get a tool on the part load adjustment screw. I have the hex head cap removed. I read in an earlier thread that the adjustment screw should be about 2 inches inside the pump housing, but I can only get a screwdriver (4mm wide blade) about an inch into it before I hit something immovable. I'm assuming this is not the adjustment screw, but as I cannot see into the hole, I have no idea. Any suggestions?

You need a really small screw driver, I mean one of those really small ones, about four inches long to access the part load screw. A four mm wide blade is probably too wide to get at it, you need more like 2mm .You have to push in firmly and turn. You will feel it when it catches and you will feel very distinct clicks when you do. With the factory spec blade, I could never get a handle on it , it just would not give me the right angle. When I say blade I mean the long thin stemmed screw driver.

As far as the thermostat goes, can't really tell what's going on with your photo, but I have taken a few apart and studied them. Pretty much you want to go just as the diagram indicates, and as far as the thermal discs go you want them ordered like this ()()()()()()()()(). They're all the same.

Ed,
Thanks for the replies. I guess my major concern is whether or not I have too many spacers (the things labeled thick and thin spacers on the above diagram). Its is clearly stated on that diagram that there are more thermal discs than what is shown, but it doesn't say anything about the spacers. Are there just 2 (one thick and one thin), or could there be more.

I can't really tell from the picture, but those are all spacers? None of them are thermal discs? I know the ones I've examined are just like the diagram, one thick and one thin. Over the years a lot of people modify these things, usually by subtracting the number of discs. You can read a fair amount of posts in this forum regarding people who take that approach. I think it's not a good idea. You can achieve the same effect by simply adjusting the rack. Maybe the previous owner subtracted some discs and replaced them with spacers.

PLEASE CORRECT ME WHERE I AM WRONG! And there are probably several points in error here.

The thermostat works by bi-metal discs retracting the rod when cold and extending it as it heats up until the linkage in the pump hits a stop. That is the point where the thermostat no longer affects the mixture. The specs call for that to happen at 113F to 127F depending on model. Any further heating of the bi-metal expansion discs just causes compression of the spring in the thermostat.

Note: If you remove the thermostat, the pump goes full rich. If you almost fully depress the little lever in the pump there is no “thermostat enrichment.”

Now for the hard part.

When cold, the thermostat rod is not extended as much. The thermostat rod must have appropriate contact with the little lever in the pump. That is what determines the progressive amount of mixture enrichment depending on temperature. The shims in the thermostat are what set the amount of enrichment at a given temperature. More shims = leaner at a given temperature, less shims = richer at a given temperature.

I used to have the specs for the rod position at various temperatures. I’m sure some Pelican can post them. If you want to do some experimenting; your freezer, refrigerator and warm water work great. Ice and a hair dryer are useful diagnostic tools.

However, “The proof is in the pudding,” as they say.

The two critical features of thermostat adjustment are: The thermostat must turn off (no enrichment) as soon as possible while maintaining reasonable (even poor) performance during warm-up. The thermostat must provide sufficient enrichment in very cold weather to have the engine run at all.

The reason for the quick turn off is to prevent the oil from becoming diluted with gasoline – a major problem with MFI. The reason for making sure the cold running-warm up part is working is that is the ONLY cold enrichment for the engine. All the other stuff is cold-start only during cranking – not running. You can be on a summer tour and a cold morning in the Sierras, Rockies, or Poconos may let it fire on cranking yet not run.

So, how do you adjust it? You can have it professionally set up. Most are too rich because that is where it runs best. I recommend the “Lean worst running.” technique. The emphasis is on the word “running.” It has to run semi-satisfactorily so it warms up. Experiment with fewer shims at various temperatures until you achieve “Lean worst running.”

Here are two Porsche diagrams to talk about. The first is a cut-a-way and the second is the diagram we need. Number 4 is the thermostat (#1 in the cut-a-way.) The X is the spring in the pump that the bi-metal thermal discs over comes. Inside the spring is the stop for “no more enrichment.” This spring is not as strong as the spring in the thermostat. You can remove the right side pump cover and see how this works.

Does your #5 shim have the same fit & finish as the others? Is there one or more that don't match the others. It may be someone shimmed the thermostat to make it less effective (or not work at all.) If so, did they richen the main mixture to compensate?

Altering the disc arrangement ultimately effects how far the rod will extend. By adding non expanding shims you are going shorten the lenth. The rod only goes so far to the final warm running position. It pushes the lever on the space cam which changes the position of the control rack which is responsible for the rich/lean adjustment. This final position can be set as well with the part load screw. So ultimately no matter what you do to the thermostat, the warm running position is set by the part load screw, which controls the position of rack, which increases or decreases the volume of fuel in each of the pumps cylinders. So assuming at running temperature you've got the right setting , what is really going to be affected by an altered thermostat is the cold running condition of the engine. I would say keep the thermostat the way original engineers designed it. I meen why would you want to second guess the engineers at Porsche?

Ed, Grady:
Yes, those are all spacers. Here's another pic in which you will see the rod with the discs still on it to the left.

By the way, there are 25 pairs of thermal discs on the rod, which I think is correct based on a previous post here. So I don't think discs have been subtracted, but I'm pretty sure spacers were added. It seems like the consensus is that there were only two spacers from the factory (one thin and one thick). If anyone knows what the thickness of these spacers should be, that would be very helpful. Upon further inspection (after Grady's inquiry), #s 5 and 3 have the same fit and finish. #s 1, 2, and 4 are identical, and #6 is a slightly different diameter than the rest. Based on this, I would guess that #5 and #3 are the original spacers, but if anyone could verify that based on the thickness numbers I came up with, I would appreciate it.

Grady, since I have only owned this car for a few months, your guess is as good as mine as to why these extra spacers are there. Couldn't tell you if they richened the mixture to compensate, but I can tell you that before I removed the thermostat for cleaning, it was running rich (warm and cold). But I think it was leaning a bit as it warmed up. I have ordered a Gunson Gastester and will run some diagnostics next week when I recieve it.

My goal is to get the thermostat back in with the appropriate spacers and then adjust the mixture if needed (I'm almost positive it needed adjustment before I cleaned the thermostat). I'll know more next week. In the meantime, any additional advice will be appreciated.

What year, model is your 911?
Do you have a copy of CMA?
Have you done a search on Pelican with MFI? There is a huge amount of info there.

I would put the now clean thermostat back the way it was (all the shims.) Make sure the warm air hoses and heat exchanger are OK. Test to see if the thermostat turns all the way off. There are a couple of ways to do this; measure the temperature if the air being exhausted from the thermostat or remove the side cover from the pump and confirm the “thermostat connecting sleeve” (#4 in the cut-a-way) is fully compressed – be careful to not apply any force.
If you don’t think you are getting sufficient hot air to the thermostat, you can use a hair dryer to test. If the mixture changes, it wasn’t hot enough.

I would add several other points: 2) includes both cranking compression and cylinder leak test. These tests are best after some spirited highway (DE) driving. 3) Includes wires, cap, rotor and general proper condition of the ignition system. 6) I would also want a new fuel filter and clean the screen in the bottom of the fuel tank. 7) The condition of the nozzles has a large effect at idle and just off idle. 8) If you need to adjust the MFI pump timing, use the opportunity to replace the Gilmer belt and both toothed pulleys. You can save the old ones as road spares. 9) Correlation includes the condition of the throttle bodies. One of the important issues is that all the linkage moves off idle simultaneously.
Proper cam timing and valve adjustment are needed.
If the car has been running rich in cool-cold weather, several oil changes are necessary to get any unburned fuel out of the oil.
You should use fresh gasoline.
Test to see if there is a difference in mixture if the breather hose is disconnected from the air filter.
Depending on the car year, the evaporative emissions control system can, under some circumstances, change the apparent mixture. You should disconnect that during tests.

Oil and soot in the muffler can screw up your mixture measurements. It can take a long time to burn off.

When you go to test the nozzles, find someone with the Bosch tester and test fluid.
"
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(C) 1969 Porsche AG

John,

I am always suspicious of shims with numbers like 0.82 mm and 2.09 mm – very un-Porsche/Bosch. Ask one of the rebuilders.

Still, I would reinstall as it was and proceed with CMA next. It is very tempting to jump ahead in the sequence but following the plan will keep you out of trouble. It is very easy to get the system out of adjustment where the only recourse is to start from scratch with a pump rebuild, throttle body rehab, and more.

I will speculate (only my guess) that if there are extra shims, a PO did that to reduce oil dilution. The main mixture was set richer to cover up the poor running during warm-up. This results in rich running all the time (the engine runs well when too rich, just not correctly.) Finally the idle may have been reset.
You can see if you start changing things without CMA, you might not be able to get back where you are now.

Grady, the car is a '72 T. I do have CMA and other articles I have printed out from the tech section. I've also read all the pertinent threads I could find on this BBS. Thanks for the advice. I will try putting it back together as you suggested.

Hey John, The thermostats I've seen have been just as the drawing indicates. One very thin washer and one very thick spacer. I think the previous owner added the additional shims to compensate for discs he may have removed? Try doing this. assemble the thermostat with your thick spacer and one thin washer. Once assembled, shake it to see if the discs are in anyway loose or rattle in the assembly. All the shims can do as far as thier function is to increase the compression of the discs, perhaps to compensate for a tired spring or again because discs were removed. If there is movement of the discs or rattling I would be suspicious of either scenario. As far as the proper functioning of the thermostat I think the critical thing is the proper number of thermal discs to give the full extension of the rod and thereby achieving the full range of the rich/lean spectrum. If there is no play or rattling of discs with only the washer and the spacer then you're probably fine. I think just to be safe I would do a little research and find out just how many discs there are. Do like I did when I was having problems wilth my thermostat, go out and get another one just to compare.

John,
Dumb ‘ol me. I suppose I could have looked at your signature line.
What is the condition of your left heat exchanger and thermostat warm air hoses? No mice?

Ed,
You have a good point. A PO could have replaces a couple of bi-metal discs with some spacers for some reason.
I agree, it shouldn’t rattle. That is a good easy test.
Adding shims to the thermostat causes it to have less enrichment at a given temperature and to turn off (no enrichment) sooner. Very desirable to prevent oil dilution.

To re-ask John’s original question:
Who knows how many bi-metal discs and spacers?

I found a few minor errors in my posts. I’ll edit them for clarity, tomorrow. If any one questions what I posted, PLEASE chime in. None of us wants something in the Pelican archives that isn’t correct.

Ed, Grady:
I'm a little confused when you say the discs should not rattle. As I understand it, the rod should have some play (appx 1/8"). Is this correct? The way mine is, I can make the discs rattle, or I can keep them from rattling depending on what position the rod is held in. Maybe what you mean is when the rod is in the position it would be when attached to the pump, with the spring (labeled with an X in Grady's illustration above) pushing it. In that case, the rod would be pushed into the t-stat and the discs will not rattle. Is this accurate, or are there flaws in my logic?

I think you are correct.
You are really taxing my memory here.
There should be enough bi-metal discs, spacers, and spring cup in the thermostat so the pump spring (X) slightly loads the assembly. In other words the parts aren’t free to rattle around on the shaft.

It's been a while for me too since I've tinkered with these things. But as I recall, you're right , there is a little free play in the rod , but I think one eighth inch seems a little excessive, and I certainly don't recall any ablility for them to rattle in the housing. That's why the spring is there, to keep compression on the discs and to keep them from rattling or moving about freely. I think you really need to find out some how exactly how many discs there are. Also, as far as fuel mixed with the oil, I think that's probably a problem with worn out pumps, much like worn rings in an engine where oil is allowed in the cylinders. I know my MFI set up didn't seem to have that problem.

Just thought I'd give this a monday morning bump. This thread has been extremely informative and helpful to me. Hopefully someone will chime in with some additional insight not yet mentioned. This info will surely help someone else down the road.

John, did you get the thermostat back together? How many spacers did you install?

Jamie

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Well, I put it back together as it was, installed it and started the car. It was popping alot. Then I shut it down, removed a few spacers (leaving only the 2 that I'm guessing are the originals), reinstalled it, and started the car again. No popping this time, but I think its because it had been running only a few minutes earlier. I'm planning on trying it again today with 2 spacers to see if I can tell a difference.

While I had the thermostat out, I tested it with a heat gun. It seems to be working correctly. When heated, tte shaft moved out probably a little less than 1/8".